SWB 912: Matching front & rear sway bars

[Donald T]

What is the best ratio of front to rear sway bars for a SWB (1968) 912?

I have a set of rear after-market sway bars that measure 17mm (not yet installed). My factory front sway bars are 13mm (installed).

If I install the rear sway bars should I install a larger sway bar for the front? (FYI: I have an Elephant Racing camber compensator installed in the trunk).

[Flieger]

Depends- what kind of handling balance do you like? Oversteer or understeer?

The issue is front roll stiffness compared to rear roll stiffness. This comes from both torsion bars and sway bars combined. Sway bars have a little more effect than torsion bars as far as going up a mm or two on only one bar.

If you put stiffer torsion and/or anti-sway bars in front, you increase the understeer compared to stock (which was a little understeer biased). If you stiffen the rear, you get more oversteer.

[JerryL]

I am running a 16 rear with a 19 front with a strut brace (along with many other tweeks) on my 66 912 coupe, I like it a lot!!
I will assume that you got a deal on the 17 rear, I would try it and think you would be fine with a 19 or 20 mm front bar,
looks like the std set up 1 or 3 mm larger bar in front and yes there are many other things that come into play.

Also if the location of the rear drop links are adjustable you may move them out to the longest setting on the bar to start with, it would be your sofest setting.
You should have plenty of options on 19 - 21mm front bars in the 911 used parts listings.

Regards

[912rustbucket]

JerryL...what torsion bar diameter are you running with that sway bar setup?

I have 13mm front only sway bar with stock (and original) T-bars. When I autoX, the car is fairly neutral to a little understeer but the car has a very (autox time) limiting amount of body roll as every corner is performed with the inside front wheel high in the air the outside rear almost running out of travel its sitting so low. I'm looking to reduce the excessive body roll without creating an unstable car.

Barry

[JerryL]

Running 19 & 23 basically stock, lowerd some and running 205-55-16's on all corners, externally adjustable (in the trunk) Koni's with the std koni's in the rear.

Do you have a set of wheels & tires for auto x?? i have a set of 15 x 7 cookie cutters I need to unload I will be posting soon, drop me a note if intrested.

Good luck

[912rustbucket]

So your torsion bars are stock stiffness?
How did the addition of a rear sway bar affect the handling characteristics? Mine only has the stock front 13mm.
I'm running 195-55 x15 on cookie cutters now with 6mm offsets so the front tires don't rub on the front shock towers in hard cornering

[Jaems]

Folks these cars are not 911's. The 912 is more balance than the 911. The 911 is throwing about 250-300 lbs, in the rear, around than your 912's. That was why they added weight in the front of the 911 and later lengthen the wheel base. You do not need those big stabilizers that a 911 does it is just over kill. If you have 13mm on the front of your 912. Then 12mm, in the rear, will be enough for any street 912. If you are going to dedicate the car as a race car. Then you will be using the adjustable kind of stabilizers, wider tires and adjustable trailing arms.

I have the factory standard front and rear stabilizers, torsion bars, with 185/65/15 tires and there is no lean in the corners. In fact it is almost too neutral for me. I personally like a little over steer.

[Donald T]

Jaem's comments make a lot of sense. The 912 is really very balanced compared to the 911. It is really a question of balance and function. I also agree that it would be nice to induce just a bit more oversteer into a SWB 912 with a rear bar even just for road use or occasional AX. Very few 912s had a rear factory bar so aftermarket is probably the practical way to go.

[Neil '67 911S]

Originally Posted by Jaems

I have the factory standard front and rear stabilizers, torsion bars, with 185/65/15 tires and there is no lean in the corners.

Jaems;

Whose 185/65-15 tires are you running? Brand and model please. Inflation pressure for street fore and aft too please.

Thanks!

[912rustbucket]

The 911 engine of that era is 150 pounds heavier than a 912 and it's all behind the axle. Most 912 racers I've talked to have advised me to stay away from a rear sway bar because the car will be much more prone to oversteer.

In my case, I have way too much roll for my liking with a stock setup (Front 13mm sway bar, no rear bar and stock torsion bar diameter). see video from last year http://youtu.be/vYtRAXhAxYE...my latest runs are getting close to getting it up to only two wheels which is starting to get scary.

I understand the only solution for me is to to stiffen the t-bars and then to add adjustable sway bars, front and rear, with the rear bar set on the softest setting.

I'm wondering how much the t-bars need to be stiffened to reduce the body roll while not making the ride too harsh for around town driving?

[Jaems]

I have the Bridgestones I think it was the 960 Pertenzas. I run 29lb front and 32lbs rear for all around driving. Don't need as much as the 911 in the rear less weight. I do have a SWB car.

[Jaems]

My torsion bars are the stock 912 and the front stabilizer is 13mm and the rear is 12mm. Drop the height to the Euro height and you should be similar. If you do not use those oversize tire that most folks like for looks. They are just too sticky for the old type suspensions that these car have. You will need to reenforce the contact points to handle them, without taring out in time, do to the strain and pressures.

[Neil '67 911S]

Originally Posted by Jaems

I have the Bridgestones I think it was the 960 Pertenzas. I run 29lb front and 32lbs rear for all around driving. Don't need as much as the 911 in the rear less weight. I do have a SWB car.

Could you please take a look and check which Bridgestones? I'd appreciate it.

Thanks!

[Jaems]

Re 950 They are probably discontinued by now.

[Neil '67 911S]

Originally Posted by Jaems

Re 950 They are probably discontinued by now.

Evidently they are discontinued. Thanks again for checking.

[djdsc]

I'm not a race suspension expert by any means, just a long time 912 driver. And I am an empirical tester. I don't mind changing things around to test my seat of the pants reactions. My goal was to reduce/eliminate the oversteer on my '68 running 185/65 Bridgstone's under hard driving. After installing a 13mm front bar I moved up to a 15mm front and things improved greatly. The final solution to the problem was to turn up the front Koni's from soft to one turn. No rear bar and rear Koni's still on soft.

[MichiganMike]

I dont mean to hijack this thread, but I am going to be in the same situation. I have a 15mm front bar (through-body) and an adding a 911SC 19mm rear bar along with larger torsion bars. Will I experience major understeer with this setup with my stock 912 motor? The car is still in progress of being built.

[Flieger]

That will result in much more oversteer than stock, though probably not something "dangerous" with the lighter engine. It will be more tail-happy, though.

Making the rear stiffer than the front on any car moves the balance towards oversteer- no matter where the engine is. The mass distribution and principle axis of polar mass moment of inertia will determine how much oversteer it eventually has, but with that variable constant, stiffening the rear will cause less understeer/more oversteer. Think front-engine viper drift car.

[MichiganMike]

Makes perfect sense, thanks Flieger! Maybe Ill search for a 15mm rear bar soon...

EDIT: my rear bar is a stock 18mm bar, not a 19mm.